U.S. Pat. No. 4,549,243 issued to Owen (the “Owen reference”) describes a spraying apparatus that can be held in the human hand for applications such as graphic work where it is desired that the area to which the spray is applied can be precisely controlled (Col 1, 11 5-9). The device disclosed in the Owen reference includes a reservoir that may comprise a cartridge, which may be refillable, which can be disconnected from the body member so that the reservoir can be replaced (Col 3, 11 49-52). The Owen reference discloses that the body member is provided with a contact to apply the high potential from the high voltage generator (which may be within the body member or remote therefrom) to the cartridge. If the cartridge is made of an electrically conductive material, then the high potential is conducted either directly to the nozzle or through the cartridge walls to the liquid therein and thence, by conduction through the liquid, to the nozzle (Col 4, 11 35-43). Thus, in the device of the Owen reference, electrical current is passed through the product reservoir or having the high voltage applied directly at the nozzle. Product emulsions, however, are susceptible to electrically induced separation in which the components of the product emulsion may separate. This invention will also not work in devices where high voltage is applied directly at the nozzle which would present a significant shocking hazard.
Published patent application no. GB 1996009622623 of Prenderdgast (the “Prendergast reference”) presents an electrostatic spraying device which may be used for air freshening and air purification and is capable of efficiently delivering material in small amounts and/or in a relative short duration of time (p 1, 11 1-8). The electrostatic spraying device disclosed in the Prenderdgast reference includes a delivery system that provides a means for establishing a column of product to be sprayed within a passage such that the trailing surface of the column is separated from the remainder of the material in the reservoir whereby the gap affords electrical isolation between the tip of the nozzle and reservoir (p. 6, 11 10-15). The Prendergast reference recognizes the benefit of such a system as permitting the reservoir to be earthed if desired and the part of the device housing the reservoir may be held in the hand without necessarily having to insulate the user from the material in the reservoir. Such electrical isolation of the main body of material to be sprayed from the column or slug to which voltage is applied may be particularly advantageous since the capacitance of the device during spraying can be reduced significantly (p.6, 11 17-24). The Prendergast reference, however, does not acknowledge the prevention of passing electric current, even at very small reservoirs through the product reservoir.